The subject matter disclosed herein relates to actuators and, more particularly, to devices, methods and systems for thermally activated displacement.
Various systems and devices may include components that are configured to be displaced during operation. Examples of such devices include combustion engines and elevators. In one example, gas turbines such as those used in power generation or aviation utilize a turbine “shroud” disposed in a turbine shell. The shroud provides for a reduced clearance between the tips of buckets disposed on the turbine rotor and the shroud in comparison to a clearance between the bucket tips and the turbine shell, to enhance efficiency by reducing unwanted “leakage” of hot gas over tips of the buckets. Current shroud systems employ solely segmented shrouds connected to the turbine shell and held together by, for example, turbine shell hooks. The clearance between the bucket tips and the shroud is simply driven by the thermal time constant behavior between the turbine shell and rotor/buckets. Cold-built clearances set during assembly, can be set high enough to mitigate rubbing, but tends to increase steady state operating clearances, reducing engine efficiency and output.
Other clearance control or displacement systems employ mechanical, electrical and/or electromechanical actuators, which can suffer degradation in harsh environments such as those found in gas turbines and engines.
Accordingly, there is a need for improved systems and methods for controlling displacement of devices, such as clearances between bucket tips and shrouds in a gas turbine during transient and/or steady state operation of the turbine.